Present-day naval operations take place in coastal environments as well as narrow straits all over the world. Coastal environments around the world are exhibiting a number of threats to naval forces. In particular a large number of asymmetric threats can be present in environments with cluttered backgrounds as well as rapidly varying atmospheric conditions. In these conditions the threat contrast may be low and varying, and the amount of background clutter can be severe. These conditions require the electro-optical means of detection and classification to be optimized in order to have more time to act against threats. In particular the assessment of classification means is an important issue. Beside short-range coastal paths, long-range horizontal paths with variable atmospheric conditions are of interest. The small differences between types of vessel can help us determine the classification of the vessel type. Different payloads and people on-board can be clues to the classification of the vessel. Operations in warmer environments, limiting the atmospheric transmission due to water vapour absorption, are challenging. Understanding of the impact of the different environments on the optical characteristics of threats is of great importance. For this purpose a trial was planned to assess the optical characteristics of different types of small surface vessels in a coastal environment. During this trial a number of small targets were used during different parts of the day and night. Furthermore positional as well as atmospheric characterisation was performed as ground truth information. From this data a first analysis was performed showing strong intensity fluctuation in target as well as background signal levels. At longer ranges and in coastal environments these target signals may well be hidden within the background clutter. This data is essential to feed models for the assessment of sensor performance in coastal environment.